1. Field of the Invention
This invention relates generally to circuit interrupters and, more particularly, to circuit interrupters that provide an audible and/or visual alarm when their trip mechanisms fail to actuate an operating mechanism for opening an electrical circuit in response to a fault condition.
2. Related Art
Circuit interrupters include, for example, circuit breakers, contactors, motor starters, motor controllers, other load controllers and receptacles having a trip mechanism. Circuit breakers are well known in the art and examples are disclosed in U.S. Pat. No. 5,260,676 and U.S. Pat. No. 5,293,522.
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which is heated and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature, which is attracted by the sizeable magnetic forces generated by a short circuit or fault, also unlatches or trips the operating mechanism.
In many applications, the circuit breaker also provides ground fault protection. Typically, an electronic circuit detects leakage of current to ground and generates a ground fault trip signal. This trip signal energizes a shunt trip solenoid, which unlatches the operating mechanism, typically through actuation of a thermal-magnetic trip device.
A common type of ground fault detection circuit is the dormant oscillator detector including first and second sensor coils. The line and neutral conductors of the protected circuit pass through the first sensor coil. The output of this coil is applied through a coupling capacitor to an operational amplifier followed by a window comparitor having two reference values. A line to ground fault causes the magnitude of the amplified signal to exceed the magnitude of the reference values and, thus, generates a trip signal. At least the neutral conductor of the protected circuit passes through the second sensor coil. A neutral to ground fault couples the two detector coils which causes the amplifier to oscillate, thereby resulting in the generation of a trip signal. Examples of these circuits can be found in U.S. Pat. Nos. 5,260,676 and 5,293,522.
Recently, there has been considerable interest in also providing protection against arc faults. Arc faults are intimate and high impedance faults which can be caused, for instance, by worn insulation between adjacent conductors, by exposed ends between broken conductors, by faulty connections, and in other situations where conducting elements are in close proximity. Because of their intimate and high impedance nature, arc faults do not generate currents of either sufficient instantaneous magnitude or sufficient average root mean square current to trip the conventional circuit interrupter. Even so, the arcs can cause damage or start a fire if they occur near combustible material. It is not practical to simply lower the pickup currents on conventional circuit breakers, as there are many typical loads which draw similar currents and would, therefore, cause nuisance trips. Consequently, separate electrical circuits have been developed for responding to arc faults. Examples of such circuits can be found in U.S. Pat. Nos. 5,224,006 and 5,691,869.
Ground fault protection circuits and arc fault protection circuits typically include separate associated test circuits for affirming their continued operability. Separate test switches are provided for performing the ground fault and arc fault tests, for example, as described in U.S. Pat. No. 5,459,630. Alternately, a single test actuator can be employed for conducting both tests as described in U.S. Pat. No. 5,982,593.
Proposals have been put forth, as set forth in U.S. Pat. No. 6,040,967, that a xe2x80x9clockoutxe2x80x9d device be included in ground fault interrupter circuit breakers. This device is only activated on testing of the breaker. If a failure of the tripping circuit or the sensing circuit is detected, the breaker is forced open on testing; leaving the consumer with a power outage that cannot be corrected without an electrician. This power loss will be a disincentive to test breakers; fewer breakers will be tested; and potentially more failed breakers will remain in the field. A study has been conducted that indicated some ground fault circuit interrupter receptacles and breakers may have failed in the field and may not be providing protection and the user is not doing the required periodic testing to detect these failures (NEMA field test survey).
Accordingly, an improved circuit interrupter protection system is desired that will alert a user to a failed breaker condition without disadvantaging the user by preventing the breaker from being reset.
The foregoing objective is achieved by a breaker failure annunciation system for either or both ground fault circuit interrupters or arc fault circuit interrupters that does not depend on actions taken by a consumer in order to detect a failure in either the mechanical trip mechanism or the electrical trip circuitry. A trip mechanism within the circuit interrupter that actuates an operating mechanism in response to predetermined current conditions to open the circuit interrupter""s contacts, provides an electrical output when activated. The electrical output is connected to an annunciator that supplies an alarm when the operating mechanism fails to open the contacts when actuated by the trip mechanism, to alert a user of the failed actuation.
In the preferred embodiment, the alarm is provided by a light emitting diode and/or an audible alarm. Preferably, where the interrupter includes an actuation coil in series with a fusible resister, the breaker failure annunciator system is connected in parallel with the series arrangement of the actuation coil and fusible resister.
Preferably, the annunciator is activated by the detection of a failure in either the trip mechanism, ground fault interrupter circuit or arc fault interrupter circuit and does not prevent the resetting of the circuit interrupter. In addition, in the preferred embodiment, a detection of a failure in the arc fault interruption circuit or the ground fault interruption circuit does not activate the trip mechanism.